That fragile peace is now effectively dead, and the Turkish airstrikes come amid a spiraling "vortex" of violence inside the country. Turkish police rounded up more than a thousand suspected Islamic State, PKK, and lefitst militants -- but the vast majority appeared to belong to the latter two categories, and were not jihadists. Meanwhile, Turkey forged a security pact with the United States allowing American fighter jets and armed drones to launch from the NATO air base at Incirlik.
The geopolitical map is getting complicated, so here's a guide to whom Turkey is now fighting.
The Islamic State
For many months, Western governments and local opposition groups, particularly Kurdish factions in southeast Turkey, have urged the government in Ankara to more aggressively confront the Islamic State. The extremist group has consolidated its position across stretches of war-torn Syria and Iraq in part through arms, fighters and money smuggled via Turkey's porous border.
Some critics accuse the center-right government of Turkish President Recep Tayyip Erdogan of tacitly enabling or supporting the Islamic State, partially as a bulwark against resurgent Kurdish factions on both sides of the border. Officials in Ankara, including Erdogan, reject the allegations.
They have not seen eye-to-eye with the Obama administration on its strategy in Syria. In the early stages of the country's conflict, Erdogan was the most outspoken world leader calling for the departure of Syrian President Bashar al-Assad. The White House's air campaign against the Islamic State was unsatisfactory to Erdogan and his allies, who wanted more direct international action against the Assad regime.
Now, after Turkey's sanctioning of U.S. air raids from the Incirlik base, a significant shift appears to be afoot. News of Washington and Ankara agreeing to a de facto "safe zone" on the Syrian side of the border follows Turkey's long-standing demand for an internationally monitored no-fly zone and "safe haven" in northern Syria that, among other things, would help ease the enormous burden of housing Syrian refugees.
After a suspected Islamic State suicide bomber killed dozens of youth activists in the town of Suruc last week, Turkey cracked down. It launched airstrikes on Islamic State targets and carried out sweeping arrests of suspected militants in Istanbul and other Turkish cities, including dozens thought to be linked to the Islamic State.
But hundreds more of those detained were said to belong to the PKK, a separatist faction deemed a terrorist organization by the United States and Turkey. Turkish jets also hit PKK camps in northern Iraq. Suspected PKK militants are accused of carrying out attacks on Turkish police and security personnel in the past week.
The PKK emerged in the 1980s as the main militant wing championing a separate homeland for Turkey's Kurdish minority, whose cultural identity had for decades been harshly suppressed by the Turkish state. An estimated 40,000 people died in about three decades of hostilities, until a cease-fire was announced by Abdullah Ocalan, the PKK's jailed leader, in 2013.
But Ocalan's control over the group from prison appears to have slackened, with a more hard-line wing frustrated by a stalled, ineffectual peace process and pushing for greater confrontation.
U.S. officials say the Turkish strikes on the PKK had nothing to do with Washington's coordination with Ankara over the fight against the Islamic State. But, in the rhetoric of Turkish officials, the war on the militant group and the Kurdish guerrillas is all part of a joint struggle against the terrorists in Turkey's midst.
Ideologically, the PKK could not be farther from the Islamic State: The PKK's political roots are Marxist-Leninist, and its political leadership is staunchly secularist. Images of unveiled female fighters in the ranks of the PKK — and those of other Kurdish factions — are frequently trotted out as a sign of Kurdish affinity for Western liberal values. Moreover, the PKK and other Kurdish factions have lost hundreds of soldiers in front-line clashes with the Islamic State.
Syrian Kurdish militias on the border with Turkey alleged that they, too, were being targeted by Turkey, claiming that Turkish tank shells had hit a Syrian village manned by both Free Syria Army rebels and Kurdish fighters in the People's Protection Units, also known as the YPG, injuring four. A Turkish official told Agence France-Presse that the YPG "remains outside the scope of the current military effort."
The YPG, whose political parent organization has direct ties to the PKK, is a headache for the Turkish government. The territorial gains of Syrian Kurdish militias in the past year have given wing once more to aspirations for a Kurdish homeland. In Diyarbakir, the most important majority-Kurdish city in Turkey's southeast, graffiti hailing the Syrian Kurdish factions is ubiquitous along the walls and alleys of the historic old quarter. Hundreds of Kurdish youths from Diyarbakir and the surrounding areas have left their homes to join the YPG's fight in Syria.
Last month, a spokesman for the Democratic Union Party, the YPG's political parent, said any military intervention by Turkey into Syria would be construed as an act of "aggression" by "invaders." Turkish officials, meanwhile, say the Syrian Kurds are in league with the Assad regime, a claim met largely with skepticism by outside observers and denied by the Kurds.
Another group caught in the Turkish dragnet is the DHKP-C, or the Revolutionary People's Liberation Party/Front, a Marxist extremist group that has carried out attacks on politicians and police in the past, including a suicide bombing in January. It also is classified as a terrorist group by Washington and was among a number of radical leftist groups targeted in a nationwide crackdown.
A member of the DHKP-C was slain during one of the many police raids carried out Friday. Her death spurred a weekend of riots and clashes in Istanbul's Gazi district, where anti-Erdogan sentiment runs deep. On Sunday, a police officer was shot in the chest during the unrest and died of his wounds.
The chaos comes at a time when Turkey's politicians are still struggling to form a government after elections in June saw Erdogan's ruling Justice and Development Party lose its parliamentary majority for the first time in a decade.
It lost dozens of seats to the Peoples' Democratic Party, or HDP, a motley bloc of leftists and Kurds, some directly linked to the PKK. The HDP's leader, Selahattin Demirtas, accused Erdogan and his allies on Monday of fanning the flames of a regional conflagration and whipping up anti-Kurdish feeling ahead of a potentially new round of elections.
"A temporary government with its temporary prime minister is dragging the country step-by-step into a civil war," Demirtas said.
Related on WorldViews